Navigation device for use in automotive vehicle

ABSTRACT

A navigation device provides a driver with proper instructions to which direction to drive when he approaches a junction at which an entering road branches out into two or more outgoing roads. Such instructions are generated not only based on a physical structure of the junction and road names but also based on a customary way of driving. When the entering road name is the same as the outgoing road name toward destination, a driver customarily keeps a through-traffic lane. If the outgoing road toward his destination branches out to a side opposite to the through-traffic lane, he would drive onto a wrong road. Under such situation, the navigation device according to the present invention gives a driver clear instructions to which direction he should drive.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority ofJapanese Patent Application No. 2000-123848 filed on Apr. 25, 2000, thecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a navigation device for use in anautomotive vehicle, and more particularly to a navigation device havinga function to give route guidance to a driver every time a vehicleapproaches a branching point, especially a junction, located on aplanned route.

2. Description of Related Art

A navigation device for an automotive vehicle, which locates a presentposition of a vehicle, sets a route plan and gives route guidance to adriver, is known hitherto. Usually, the located present position of thevehicle and the planned route toward destination are displayed on adisplay panel. It is also known to give voice guidance to a driver whena vehicle approaches a branching point on the planned route. Forexample, voice guidance such as “turn to right at an intersection 50meters ahead” is given to the driver. Such voice guidance is not givenat all branching points, but it is given at particular branching pointswhere it is difficult for the driver to correctly follow the plannedroute without such guidance. For example, if a minor road is simplyconnected to a main road and the driver can easily enter the main roadon the planned route without guidance, no guidance is given.

On the other hand, the guidance is given at a branching point such as ajunction where a road entering the junction branches out into two ormore roads outgoing from the junction. For example, if the outgoing roadtoward destination has the same road name as the entering road, a voiceguidance, such as “continue to proceed to the present road” or “keepdriving on the same road” is given to the driver.

The above situation will be further explained, taking an example inJapan where a left-side driving system is employed. If there are twolanes on a highway including an expressway, slow traffic moves on theleft lane and the right lane is a speed lane. When a driver approaches ajunction where a road toward his destination is directed to the rightside of the junction, he drives on the right lane on the road enteringthe junction. If the entering road has the same name as the outgoingroad toward his destination, voice guidance such as “keep driving on thesame road” would be appropriate. However, there is another situationwhere the outgoing road toward his destination has the same name as theentering road another outgoing road is directed to the right side of thejunction. In this case, if the voice guidance such as “keep driving thesame road” is given, it is possible for the driver to proceed to thewrong road branching out to the right side from the junction. If thedriver is very familiar to the structure of the particular junction, hemay not be misled. However, there is a possibility in the conventionalnavigation device to mislead the driver.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedproblem, and an object of the present invention is to provide animproved navigation device which is able to give a driver appropriateroute guidance at a branching point, especially at a junction.

A navigation device for use in an automobile vehicle is mainly composedof a vehicle position detector including a GPS receiver, a map datafeeder, a keyboard, a display panel and a speaker. A driver inputs hisdestination at a starting point. The navigation device sets a route planfrom the starting point to the destination on the map displayed on thedisplay panel. When the vehicle approaches a branching point, especiallya junction, located on the route plan, the navigation device instructsthe driver to which direction to drive. At a junction, one road enteringthe junction branches out into tow or more roads outgoing from thejunction including an outgoing road toward destination.

The navigation device determines whether the entering road has the samename as that of the outgoing road toward destination, whether a trafficsystem is a left side driving system or a right side driving system, andwhether at which side of the outgoing road toward destination the otheroutgoing roads are located. The instructions to which direction to driveare generated based on those determinations. Under the left side drivingsystem as in Japan, if the outgoing road toward destination has the samename as the entering road, the navigation device instructs to drive tothe left if the other outgoing roads are located at the right side ofthe outgoing road toward destination and to drive straight if the otheroutgoing roads are located at the left side. Under the right sidedriving system as in the U.S.A., the navigation device instructs todrive to the right if the other outgoing roads are located at the leftside and to drive straight if the other outgoing roads are located atthe right side.

If the outgoing road toward destination has a name different from thatof the entering road, it is not necessary to give special instruction asabove, because the driver is properly guided by usual instructions. Itis preferable to give the driver the instructions by means of voiceguidance in addition to the route plan displayed on the display panel.The route guidance process performed in the navigation system may bestored in a memory medium as a computer program.

A driver is properly guided by the navigation device according to thepresent invention because instructions to which direction to drivethrough a junction are generated, not only based on a physical structureof the junction and road names but also based on a customary way ofdriving. Under the left side driving system, a driver usually keepsright when he drives through a junction if an outgoing road towarddestination has the same name as the entering road. Therefore, if theoutgoing road toward destination extends leftward under such situation,the instructions to drive to the left are very helpful to the driver. Onthe other hand, if the outgoing road toward destination is located atthe right side of the junction, the instructions to drive straight leadthe driver to the proper direction. The same is applicable to the rightside driving system though the left and the right are reversed.

Other objects and features of the present invention will become morereadily apparent from a better understanding of the preferred embodimentdescribed below with reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram showing an information center for supplyingvarious pieces of traffic information to a navigation device mounted onan automotive vehicle;

FIG. 1B is a block diagram showing a navigation device mounted on anautomotive vehicle;

FIG. 2 is a flowchart showing a route guidance process performed in thenavigation device;

FIG. 3 is a flowchart showing a guidance process at a branching pointperformed in the navigation device; and

FIGS. 4A-4C are examples of junctions where the route guidance is givento a driver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described withreference to the drawings. First, referring to FIG. 1B, an entirestructure of a navigation device which is able to communicate with aninformation center shown in FIG. 1A will be described. The navigationdevice 20 includes a vehicle position detector 22, a map data feeder 24,a group of switches 26, a remote controller sensor 27, a display panel28, a speaker 30, an outside memory 32, a communication device 34, andelectronic controller 36.

The vehicle position detector 22 is composed of known components: agyroscope 38, a vehicle speed sensor 40, a GPS receiver 42 whichreceives radio waves from a GPS system. Since each of those componentsincludes certain detection errors, plural components are used foraccurately detecting the vehicle position by supplementing errors.However, it is not always necessary to use all of those components. Aterrestrial magnetism sensor, a rotational angle sensor for a steeringwheel, or a wheel rotational sensor may be used in addition to or inplace of certain components.

The map data feeder 24 feeds map data stored in a memory medium to theelectronic controller 36. The map data include data showing roadconnections (road network data), data for map matching for improvingaccuracy of vehicle position detection. As the memory medium storing themap data, a CD-ROM or a DVD is usually used, but a memory card or othermedium may be used. The road network format includes link information,node information and inter-link connection information. The linkinformation includes: link IDs for identifying respective links;link-classes for differentiating an expressway, a toll road, a usualhighway, an added road and so on from one another; and informationregarding a link itself such as data showing coordinates of a beginningand end points of a link and data showing a link length. The nodeinformation includes: node IDs for identifying respective nodesconnecting links; information regarding regulations such as no-left-turnor no-right-turn at an intersection; and information as to whether atraffic signal is equipped or not at a particular intersection. Theinter-link connection information includes information such as one-waytraffic and traffic prohibition due to construction or other reasons.There are situations where traffic is allowed to enter a certain linkfrom one link but is prohibited to enter it from the other link.Accordingly, the traffic condition in a particular link is determined bythe inter-link connection situation.

The group of switches 26 includes various switches for operating thenavigation device 20, such as switches for changing displays on thedisplay panel 28 and switches for inputting a destination and otherinformation necessary to determine a planned route. The switches forchanging the displays may be touch-switches formed integrally with thedisplay panel 28 or may be mechanical switches. The remote controllersensor 27 receives signals sent from a remote controller 27 a operatedby a user. The navigation device 20 is operated either by the group ofswitches 26 or the remote controller 27 a.

The display panel 28 displays thereon a map fed from the map data feeder24, a mark showing a present vehicle position fed from the vehicleposition detector 22, and a route plan set by the navigation device. Theroute plan is overlapped on the map shown on the display panel 28. Thespeaker 30 announces voice guidance in addition to a route guidanceshown on the display panel 28. For example, voice guidance such as “turnto right at the next intersection” is given to the driver. Since thedriver is guided by the voice, he can drive more safely without lookingat the display panel.

The outside memory 32 stores therein the route plan set by theelectronic controller 36, and the stored memory is backed up by a powersource (not shown). The communication device 34 receives information(e.g. information for Vehicle Information and Communication System—VICS)sent from the information center 10, and transmits information tooutside devices or systems. The information received by thecommunication system 34 is processed in the electronic controller 36. Asthe communication device 34, an automobile phone or a mobile phone maybe used, or other devices specialized for this purpose may be used. Theelectronic controller 36 is composed of a known computer including CPU,ROM, RAM, I/O, and bus lines connecting those components. The electroniccontroller 36 controls the display panel 28, the speaker 30, the outsidememory 32 and the communication device 34, based on inputs fed from thevehicle position detector 22, the map data feeder 24, the switches 26and the remote controller sensor 27.

The structure of the information center 10 shown in FIG. 1A will bebriefly explained. The information center 10 is composed of: aninformation collector 12 for collecting outside information such astraffic jam or regulations fed from roadside sensors S; a road networkdata memory 14 that stores road maps of an area covered by theinformation center and various traffic and road information collected bythe information collector 12; a communication device 16 that wirelesslycommunicates with the navigation device 20; and a controller 18 thatspecifies particular roads under certain regulations, traffic jam and soon, based on vehicle position data sent from the navigation device 20and information fed from the information collector 12. The controller 18controls an entire operation of the communication center 10.

The navigation device 20 described above operates in the followingmanner. First, a driver inputs his destination using the switches 26.The electronic controller 36 automatically sets a route plan, which ismost appropriate, from the starting point to the destination anddisplays the route plan on the display panel 28. The driver is alsoguided by voice guidance given through the speaker 30. The process ofsetting the route plan and the process of route guidance will bedescribed in detail with reference to FIGS. 2 and 3.

Referring to FIG. 2, upon starting the process, the route plan from thestarting point to the destination fed by the driver is set at step S10.That is, the driver inputs his destination based on the road map shownon the display panel 28. The starting point is determined based on thedata sent from the GPS receiver 42. Then, the driving route from thestarting point to the destination is calculated, based on Dijkstramethod, to make the route shortest and most economical. Then, theprocess proceeds to step S20, where the route guidance is started andthe driver drives according to the guidance. At step S30, a presentposition of the vehicle driving on the planned route is calculated basedon the data fed from the vehicle position detector 22. At step S40, mapdata from the present position to a point having a certain distance fromthe present position are obtained.

Then, at step S50, whether or not the next branching point located onthe planned route is a branching point that requires route guidance(referred to as a branching point guidance). When the branching pointguidance is performed, the driver is instructed by the navigation deviceas to which direction he should drive to pass the branching point. Suchguidance is not required at all branching points. Therefore, thebranching points at which the guidance is required are selected fromamong all the branching points, considering particular structures ofeach branching point and other conditions. All the junctions arecategorized in a branching point group requiring guidance. A branchingpoint where a driver can easily drive through without specialinstructions is categorized in a group requiring no guidance. Forexample, if two roads cross each other with a substantially right angleand a planned route is set to drive straight, no special guidance isrequired. Another example: if a planned route is a main road curving atan intersection where a minor road crosses the main road, the drivereasily drives through the intersection along the main road withoutspecial guidance. The link-class mentioned above relates to judgment asto whether a road is a main road or a minor road. This link-class is setin the road network data fed from the map data feeder 24.

If it is determined that the next branching point is a branching pointrequiring guidance at step S50, the process proceeds to step S60. Theroute guidance performed at step S60 (branching point guidance) will beexplained later in detail with reference to FIG. 3. Then, the processproceeds to step S70, where other information ancillary to the routeguidance given at the branching point is given to the driver. If it isdetermined that the next branching point is not a branching pointrequiring guidance at step S50, the process proceeds to step S70,skipping step S60. At step S80, whether the vehicle has arrived at thedestination is determined. If the vehicle has arrived at thedestination, the entire process completed. If not, the process movesback to step S50 to repeat the steps following step S50.

The branching point guidance performed at step S60 will be described indetail with reference to FIG. 3. At step S110, whether the nextbranching point is a junction is determined. If the next branching pointis a junction, the process proceeds to step S120. If not, the processmoves to step S210, where a usual guidance is given to the driver. Thatis, instructions such as “turn left,” “turn right” or “proceed straight”are given.

If it is determined that the next branching point is a junction at stepS110, the process proceeds to step S120. At a junction, a road enteringthe junction branches out into two or more roads outgoing from thejunction, and one of the outgoing roads is a road toward destination. Atstep S120, whether the outgoing road toward destination is a main roador an auxiliary road connected to a main road is determined. If theoutgoing road toward destination is the auxiliary road, the processproceeds to step S130, where the name of the main road connected to theauxiliary road is set as the name of the outgoing road towarddestination. Then, the process proceeds to step S140. If it isdetermined that the outgoing road toward destination is a main road atstep S120, the process proceeds to step S140, skipping step S130.

At step S140, whether or not the name of the entering road is the sameas the name of the outgoing road toward destination is determined. Ifthe name of the outgoing road toward destination is different from thatof the entering road, the process proceeds to step S210, where the usualguidance described above is given to the driver. If the entering roadhas the same name as the outgoing road toward destination, the processproceeds to step S150, where whether the traffic system is a right sidedriving system or a left side driving system is checked.

If the traffic system is the left side driving system, then the processproceeds to step S160, where whether the outgoing roads other than theoutgoing road toward destination are located at the right side of theoutgoing road toward destination or at the left side thereof isdetermined. If the other outgoing roads are located at the right side ofthe outgoing road toward destination, the process moves to step S170,where the driver is instructed to proceeds to the left side. If theother outgoing roads are located at the left side, the process moves tostep. S180, where the driver is instructed to “KEEP THE SAME ROAD” onwhich he is now driving. The instruction to keep the same road isindirect guidance to proceeds to the right. Reasons for this will befurther explained later with reference to some examples of junctions.

On the other hand, if it is determined that the traffic system is theleft side driving system at step S150, the process moves to step S190,where whether the other outgoing roads are located at the left side orat the right side of the outgoing road toward destination is determined.If the other outgoing roads are located at the left side, the processproceeds to step S200, where the driver is instructed to proceed to theright side. If the other outgoing roads are located at the right side,the process moves to step S180, where the driver is instructed to keepthe same road on which he is now driving.

Now, referring to FIGS. 4A, 4B and 4C, some examples of the junctionsand guidance which is given at respective junctions will be explained.In the example shown in FIG. 4A, the road entering the junction branchesout into two roads outgoing from the junction. One of the outgoing roadsis the outgoing road toward destination, and those three roads are allexpressways. Those roads are named as follows: the entering road as “A”,the outgoing road toward destination as “A” which is the same as theentering road (YES at S140), and the other outgoing road as “B”. Thetraffic system is the left side driving system (YES at S150), and theother outgoing road is located at the right side of the outgoing roadtoward destination (YES at S160). As the driver approaches thisjunction, he is instructed to “PROCEED TO LEFT” at step S170.

Under the left side driving system as in Japan, it is customary to keepright on the entering road when a route plan indicates that a drivershould proceed to an outgoing road having the same name as the enteringroad. At the junction as shown in FIG. 4A, however, the outgoing roadtoward destination (which has the same road name “A” as the enteringroad) branches out to the left side at the junction. Therefore, it isvery helpful or even necessary to instruct the driver to “PROCEED TOLEFT” when he approaches such junction as shown in FIG. 4A. If aninstruction to “KEEP THE SAME ROAD” were given under this situation,taking into consideration only the road name “A”, such an instructionwould mislead the driver. For the same reason, the driver is instructedto “PROCEED TO LEFT” even if the outgoing road “A” extends straight fromthe entering road “A” and the other outgoing road “B” branches out tothe right side. In other words, the guidance is not given solely basedon a physical structure of a junction, but a customary way of driving isalso taken into consideration.

In the example shown in FIG. 4B, an entering road “A” branches out intotwo roads, an outgoing road “A” toward destination and the otheroutgoing road “B”. The route plan teaches the driver to keep the sameroad “A” through the junction (YES at S140). The traffic system is theleft side driving system (YES at S150), and the other outgoing road “B”is located at the left side of the outgoing road “A” (NO at S160). Asthe driver approaches this junction, he is instructed to “KEEP THE SAMEROAD”. It is appropriate to give such an instruction to the driverbecause he customarily keeps right on the entering road under thissituation.

The example of FIG. 4C shows a similar situation as that of the exampleshown in FIG. 4B, except that the other outgoing road “B” extendsstraight from the entering road “A” and is located at the left side ofthe outgoing road “A” toward destination. As the driver approaches thisjunction, he is instructed to “KEEP THE SAME ROAD” even though theoutgoing road toward destination extends to the right side of thejunction. It is appropriate to give such an instruction to the driverbecause he customarily keeps right on the entering road under thissituation.

Under the left side driving system as in Japan, the instruction to“PROCEED TO LEFT” is given only when the other outgoing roads arelocated at the right side of the outgoing road toward destination. Underthe right side driving system as in the U.S.A., the instruction to“PROCEED TO RIGHT” is given when the other outgoing roads are located atthe left side of the outgoing road toward destination. For example, ifthe junction shown in FIG. 4B is in the right side driving system, theinstruction to “PROCEED TO RIGHT” is given, because the entering roadand the outgoing road toward destination are commonly named as “A” (YESat S140) and the other outgoing road “B” is located at the left side(YES at S190). If an instruction to “KEEP THE SAME ROAD” were givenunder this situation, taking into consideration only the physicalstructure of the junction, such an instruction would mislead the driver,because it is customary to keep left on the entering road “A” under thissituation. Similarly, at the junction shown in FIG. 4C, the instructionto “PROCEED TO RIGHT” is given.

At the junctions exemplified in FIGS. 4A, 4B and 4C, a four-laneentering road branches out into two two-lane outgoing roads. However,the number of the lanes is not limited to those. The entering road andthe outgoing roads may have the same number of lanes. The important isto generate guidance which is most helpful to a driver, taking intoconsideration not only a physical structure of a junction and road namesbut also a customary way of driving.

While the present invention has been shown and described with referenceto the foregoing preferred embodiment, it will be apparent to thoseskilled in the art that changes in form and detail may be made thereinwithout departing from the scope of the invention as defined in theappended claims.

What is claimed is:
 1. A navigation device for use in an automotivevehicle comprising: means for setting a route plan from a starting pointto a destination; and means for generating route guidance when thevehicle approaches a junction, located on the route plan, where a roadentering the junction branches out into two or more roads outgoing fromthe junction, one of the outgoing roads being set as an outgoing roadtoward destination on the route plan, wherein: the route guidance givesa driver instructions as to which direction to drive through thejunction, based on information as to at which side of the outgoing roadtoward destination the other outgoing roads are located, if the outgoingroad toward destination has a same name as that of the entering road;wherein the instructions as to which direction to drive are determinedalso based on a traffic system, a left side driving system or a rightside driving system.
 2. The navigation device as in claim 1, wherein:under the left side driving system, the route guidance givesinstructions to proceed left if the other outgoing roads are located ata right side of the outgoing road toward destination and givesinstructions to proceed straight if the other outgoing roads are locatedat a left side of the outgoing road toward destination.
 3. Thenavigation device as in claim 1, wherein: under the right side drivingsystem, the route guidance gives instructions to proceed right if theother outgoing roads are located at a left side of the outgoing roadtoward destination and gives instructions to proceed straight if theother outgoing roads are located at a right side of the outgoing roadtoward destination.
 4. The navigation device as in claim 1, wherein: theroute guidance generating means determines that the outgoing road towarddestination has the same name as the entering road, if the outgoing roadtoward destination is an auxiliary road connected to a main road havingthe same name as that of the entering road.
 5. The navigation device asin claim 1, wherein: the route guidance generating means furthergenerates route guidance when the vehicle approaches a branching pointother than the junction.
 6. The navigation device as in claim 5,wherein: the route guidance generating means determines whether routeguidance is required at the branching point.
 7. The navigation device asin claim 1, further including a voice sound generator, wherein: theinstructions to the driver is given by means of the voice sounds.
 8. Aprocess of navigating a driver, the process comprising steps of: settinga route plan from a starting point to destination; determining whether abranching point ahead located on the route plan is a junction at which aroad entering the junction branches out into two or more outgoing roadsincluding an outgoing road toward destination; determining whether aname of the entering road is the same as a name of the outgoing roadtoward destination; determining whether a traffic system is a left sidedriving system or a right side driving system; and giving the driverinstructions to which direction to drive through the junction based oninformation as to at which side of the outgoing road toward destinationthe other outgoing roads are located and information as to the trafficsystem, if the name of the entering road is the same as the name of theoutgoing road toward destination.
 9. A memory medium storing a computerprogram for performing the process recited in claim
 8. 10. A navigationsystem for use in an automotive vehicle having a right side drivingsystem, the navigation system comprising: a device for setting a routeplan from a starting point to a destination; and a device for generatingroute guidance, wherein: when the vehicle approaches a junction locatedon the route plan, and a road entering the junction branches out intotwo or more roads outgoing from the junction, one of the outgoing roadsbeing set as an outgoing road toward destination on the route plan, andwhere the outgoing road toward destination and the entering road haveidentical names, the route guidance provides a driver with instructionsas to which direction to drive based on a location of the road towarddestination relative to the other outgoing roads.
 11. The navigationsystem as in claim 10, wherein if the outgoing road toward destinationis left relative to the other outgoing roads, the route guidanceprovides the driver with instructions to lead the driver to the outgoingroad toward destination without specifying that the outgoing road towarddestination is located to the left of the other outgoing roads.
 12. Thenavigation system as in claim 11, wherein the route guidance providesthe driver with instructions to remain in a lane in which the driver iscurrently driving.
 13. The navigation system as in claim 10, wherein ifthe outgoing road toward destination is located right relative to theother outgoing roads, the route guidance provides the driver withinstructions to lead the driver to the outgoing road toward destinationby specifying that the outgoing road toward destination is located tothe right of the other outgoing roads.
 14. The navigation system as inclaim 10, wherein the junction is a junction located either on anexclusive road for automobiles or on an expressway.
 15. The navigationsystem as in claim 10, wherein the route guidance generating devicedetermines that the outgoing road toward destination has a nameidentical to that of the entering road, if the outgoing road towarddestination is an auxiliary road connected to a main road having a nameidentical to that of the entering road.
 16. The navigation system as inclaim 10, wherein the route guidance generating device further generatesroute guidance when the vehicle approaches a branching point other thanthe junction.
 17. The navigation system as in claim 16, wherein theroute guidance generating device determines whether route guidance isrequired at the branching point.
 18. The navigation system as in claim10, further including a voice sound generator for providing the driverwith vocal instructions.
 19. A navigation system for use in a right sidedriving system type automotive vehicle, the navigation systemcomprising: a device for setting a route plan from a starting point to adestination; a route guiding device for giving a driver instructions asto which direction to drive when the vehicle approaches a junctionlocated on the route plan, where a road entering the junction branchesout into an outgoing road toward destination and other outgoing roads; afirst judging portion for judging whether the outgoing road towarddestination has a name identical to that of the entering road; and asecond judging portion for judging at which side of the other outgoingroads the outgoing road toward destination is located if the firstjudging portion judges that the outgoing road toward destination has thename identical to that of the entering road, wherein: the route guidingdevice provides the driver with instructions as to which direction todrive through the junction based on judgments made by the second judgingportion.
 20. The navigation system as in claim 19, wherein if theoutgoing road toward destination is located left relative to the otheroutgoing roads, the route guiding device provides the driver withinstructions to lead the driver to the outgoing road toward destinationwithout specifying that the outgoing road toward destination is locatedto the left of the other outgoing roads.
 21. The navigation system as inclaim 20, wherein the route guiding provides the driver withinstructions to remain in a lane in which the driver is currentlydriving.
 22. The navigation system as in claim 19, wherein if theoutgoing road toward destination is located right relative to the otheroutgoing roads, the route guiding device provides the driver withinstructions to lead the driver to the outgoing road toward destinationby specifying that the outgoing road toward destination is located tothe right of the other outgoing roads.
 23. The navigation system as inclaim 19, wherein the junction is a junction located either on anexclusive road for automobiles or on an expressway.
 24. The navigationsystem as in claim 19, wherein the first judging portion determines thatthe outgoing road toward destination has the name identical to that ofthe entering road if the outgoing road toward destination is anauxiliary road connected to a main road having the name identical tothat of the entering road.
 25. The navigation system as in claim 19,wherein the route guiding device further provides the driver withinstructions when the vehicle approaches a branching point other thanthe junction.
 26. The navigation system as in claim 25, wherein theroute guiding device determines whether route guidance is required atthe branching point.
 27. The navigation system as in claim 19, furtherincluding a voice sound generator for providing vocal instructions tothe driver.
 28. A right side driving system based navigation method,comprising: setting a route plan from a starting point to a destination;determining whether a branching point located ahead on the route plan isa junction at which a road entering the junction branches out into twoor more outgoing roads including an outgoing road toward destination;determining whether a name of the entering road is identical to that ofthe outgoing road toward destination; determining to which side of theother outgoing roads the outgoing road toward destination is located;and providing a driver with instructions as to which direction to drivethrough the junction based on a location of the outgoing road towarddestination relative to the other outgoing roads.
 29. The method ofclaim 28, wherein if the outgoing road toward destination is locatedleft of the other outgoing roads, providing instructions to lead thedriver to the outgoing road toward destination without specifying thatthe outgoing road toward destination is located to the left of the otheroutgoing roads.
 30. The method of claim 28, further comprisinginstructing the driver to remain in a lane in which the driver iscurrently driving.
 31. The method of claim 28, wherein if the outgoingroad toward destination is located right of the other outgoing roads,providing instructions to lead the driver to the outgoing road towarddestination by specifying that the outgoing road toward destination islocated to the right of the other outgoing roads.
 32. A right sidedriving system based navigation method, comprising: setting a route planfrom a starting point to a destination; identifying a junction locatedon the route plan at which an entering road branches out to two or moreoutgoing roads, one of which is an outgoing road toward destination;determining whether a name of the entering road is identical to that ofthe outgoing road toward destination when the driver approaches thejunction; determining at which side of the other outgoing roads theoutgoing road toward destination is located; and providing a driver withinstructions as to which direction to drive through the junction basedon a location of the outgoing road toward destination relative to theother outgoing roads.
 33. The method of claim 32, wherein: if it isdetermined that the outgoing road toward destination is located left ofthe other outgoing roads, providing instructions to lead the driver tothe outgoing road toward destination without specifying that theoutgoing road toward destination is located to the left of the otheroutgoing roads.
 34. The method of claim 33, further comprisinginstructing the driver to remain in a lane in which the driver iscurrently driving.
 35. The method of claim 32, wherein if it isdetermined that the outgoing road toward destination is located right ofthe other outgoing roads, providing the instructions to lead the driverto the outgoing road toward destination by specifying that the outgoingroad toward destination is located to the right of the other outgoingroads.